Travel to two countries (Japan and Taiwan) or prioritise one country for a longer stay?

I will be in Mainland China for work later in the year and I’m looking to take advantage of being in Asia before heading home to Europe.

I spent two weeks in Japan last year (Osaka, Kyoto, Tokyo and Sapporo) and had the absolute best time. I definitely want visit again and I’ve heard great things about Sendai so I’ve chosen to pair a few days there with some time in Tokyo before flying to Taipei, another place I’ve always wanted to visit.

I’m pretty happy with my basic travel itinerary below, but I’m wondering if anyone has done a similar trip or thinks it would be better to prioritise one place instead of both Japan and Taiwan? I honestly don’t know if I’m unnecessarily trying to squeeze any time I can get in Japan and sacrificing more extensive travel in Taiwan…

Saturday 10/10 - Travel to Tokyo from Beijing early in the AM. Arrive in Tokyo and take the bullet train to Sendai.
Sunday 11/10 - Sendai
Monday 12/10 - Sendai
Tuesday 13/10 - Sendai/Travel to Tokyo later in the day
Wednesday 14/10 - Tokyo
Thursday 15/10 - Tokyo
Friday 16/10 - Tokyo/Travel to Taipei later in the day
Saturday 17/10 - Taipei
Sunday 18/10 - Taipei
Monday 19/10 - Taipei
Tuesday 20/10 - Taipei
Wednesday 21/10 - Taipei/Fly home in the evening